US3526684A

US3526684A - Separation of cokes into needle-like and non-needle-like particles and the production of carbon or graphite bodies

Info

Publication number: US3526684A
Application number: US666170A
Authority: US
Inventors: Leroi E Hutchings
Original assignee: Great Lakes Carbon Corp
Current assignee: SGL Carbon Corp
Priority date: 1967-09-07
Filing date: 1967-09-07
Publication date: 1970-09-01
Anticipated expiration: 1987-09-01
Also published as: FR1587364A; GB1194985A; ES357911A1; DE1796147A1

Description

Sept. 1, 1970 LE ROI E. HUTCHINGS SEPARATION OF COKES INTO NEEDLE-LIKE AND NON-NEEDLE-LIKE PARTICLES AND THE PRODUCTION OF CARBON OR GRAPHITE BODIES Filed Sept. 7. 1.967

CALCINED COKE, SOME OF WHICH HAS A NEEDLE-LIKE STRUCTURE SCREEN TO SEPARATE THE MINUS 3 TYLER MESH GRIND THE PLUS 3 TYLER MESH TO MINUS 3 TYLER MESH SCREEN TO SERIES OF NARROWLY SIZED PARTICLE FRACTIONS, FOR EXAMPLE "3/ *6, '6/8, "8/*IO,'IO/*I6 a '20l'35 TYLER MESH MECHANICALLY SEPARATE THE NEEDLE-LIKE PARTICLES FROM THE NON-NEEDLE-LIKE SUBSTANTIALLY ROUND AND SUBSTANTIALLY CUBICAL PARTICLES I IRIND THE SEPARATED NEEDLE-LIKE I PARTICLES,OR A PORTION OF SAME, INTO A CARBONACEOUS FLOUR, E6. I

| 50% 2% MINUS 200 MESH TYLER GRIND THE SUBSTANTIALLY ROUND 8 SUBSTANTIALLY CUBICAL PARTICLES INTO A CARBONACEOUS FLOUR,E.G. 50/$ 2/o MINUS 200 MESH TYLER I I IA I I MIX THE SEPARATED NEEDLE-LIKE PARTICLES WITH A CARBONIZABLE BINDER,8 TYPICALLY ALSO WITH A CARBONACEOUS FLOUR FILLER (SUCH AS THAT OBTAINED BY GRINDING THE SEPARATED NON-NEEDLE-LIKE PARTICLES) EXTRUDE THE MIXTURE INTO A GREEN BODY BAKE THE EXTRUDED .GREEN BODY I L I G RAPHITIZE THE BAKED I United States Patent SEPARATION OF COKES INTO NEEDLE-LIKE AND NON-NEEDLE-LIKE PARTICLES AND THE PRO- DUCTION OF CARBON OR GRAPHITE BODIES LeRoi E. Hutchings, Mount Prospect, Ill., assignor to Great Lakes Carbon Corporation, New York, N.Y.,

a corporation of Delaware Filed Sept. 7, 1967, Ser. No. 666,170

Int. Cl. C01b 31/04 US. Cl. 264-29 20 Claims ABSTRACT OF THE DISCLOSURE Calcined cokes, which contain fractions of needle-like and non-needle-like particles, are separated into two fractions each of which is more valuable for certain end uses than the original material.

Special carbon or graphite bodies having a high degree of anisotropy are produced by using carbonaceous particles in their production which are predominantly or exclusively needle-like. The needle-like particles are obtained by mechanical separation from a. starting material consisting of calcined coke particles, some of which are needle-like and the remainder of which possess other shapes, such as round, or cubical etc. After the needle-like particles are separated from the otherwise shaped calcined coke particles, they are mixed with a carbonizable binder and extruded. They are then either baked or graphitized depending upon the end product desired. The non-needle-like particles are particularly useful in the production of some types of anodes, some mold stocks and in the production of graphite articles for nuclear applications. They also are highly useful for the preparation of a carbonaceous flour along with the separated needle-like particles to make the carbon or graphite bodies having a high degree of anisotropy, because in grinding the non-needle-like particles a large amount of needle-like flour is generated.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to a unique process for the separation of cokes into needle-like particles and into nonneedle-like particles from calcined cokes which contain a fraction of each.

This invention also relates to a unique process for making carbon or graphite bodies. The invention relates most particularly to a novel method of making carbon or graphite bodies having a high degree of anisotropy, or low thermal expansion in the axial direction involving the alignment of needle-coke particles by extrusion or other forming techniques. Extruded carbon bodies having a high degree of anisotropy are particularly suitable in applications where conduction of electricity with minimum power losses is desired, e.g. in electrical furnaces and cells used in the metallurgical industries. Graphite bodies having a high degree of anisotropy are particularly useful as graphite electrodes for electric furnaces in the production of steel and other metals. In such use, electrode trains (viz a number of electrodes coupled to each other by means of threaded sockets and connecting nipples and mechanically suspended from the top of the furnace) are typically employed. 'It is important that the thermal expansion and resistivity of the individual electrodes in the train be kept as low as possible in the axial direction of the train in order to minimize power losses and mechanical problems. Graphite bodies having a high degree of anisotropy or low thermal expansion are also particularly suitable for use as the aforementioned nipples.

3,526,684 Patented Sept. 1, 1970 Description of the prior art The making of such carbon or graphite bodies or electrodes having a high degree of anisotropy in the axial direction and using needle-type calcined coke (e.g. coke from delayed coker raw petroleum coke) has already been described in the art, such as in US. Pat. 2,775,549. This patent also discusses the advantages of such electrodes, such as lower C.T.E. (coefficient of thermal expansion) and resistivity, as compared to electrodes made from amorphous petroleum coke. The subject matter of that patent, however, pertains solely to techniques for obtaining needle-like coke from a petroleum residuum. In order to obtain a high yield or high percentage of needle-like coke by coking a petroleum residuum, it is generally necessary to alter the operations at the oil refinery somewhat, with the result that extra processing is necessary, and/or lower gasoline and gas oil yields are obtained. Such extra processing and product losses, of course, increase the cost that the purchaser has to pay for the needle-like coke as compared to regular coke.

.The terms regular and needle-like when used in the foregoing sense are meant to refer to the degree or percentage of needle-like structure or particles possessed by the coke and this is typically measured by the degree of anisotropy or the C.T.E. in the axial direction of graphite articles made from the coke. For example, graphite articles made from needle-like coke may typically possess a C.T.E. of 4 to 8 10-' inches/inch/C., whereas those made from regular coke may typically possess a C.T.E. of 15 to BOX 10- inches/inch/ C, When measured over the same temperature range in the axial direction. The foregoing C.T.E. values and any that follow are the mean coefficients of thermal expansion measured over the temperature range of 20 C. to C.

Some regular cokes are more anisotropic than others and graphite articles made from same may possess a C.T.E. of 10 to l2 10-' inches/inch/C. rather than the aforesaid typical C.T.E. of 15 to 30 10-' inches/ inch/ C. A coke yielding a graphite article with a C.T.E.

between 10 and about 12x10" inches/inch/C. would not be considered a good needle-like coke if used for the purpose of making anisotropic graphite bodies and yet it is considerably better than a typical regular coke if used for such purposes.

SUMMARY OF THE INVENTION It is a discovery of the present invention that it is possible to upgrade both regular cokes having a C.T.E. between about 10 and about 12 10 and needle-like cokes into two fractions, each fraction being more valuable for certain purposes than the original starting coke material. This upgrading of the coke in the present invention is carried out by means of a post-coking and post-calcining mechanical operation wherein needlelike coke particles are separated from non-needle-like coke particles contained in a batch of calcined coke containing both types of particles. The invention is particularly applicable to and later exemplified by calcined coke derived from delayed coker raw petroleum coke. However, its principles may advantageously be applied to any anisotropic calcined coke (e.g. coke which contains needle-like particles) regardless of source. Such cokes also include coke made from purified coal tar residues and coke made from aromatic residues resulting from cracking petroleum fractions in petrochemical operations, e.g. residues from naphtha cracking to produce ethylene.

These mechanically separated needle-like coke particles are then used as part or all of the aggregate in the extrusion step of making anisotropic carbon or graphite bodies. This procedure and the advantages of same are founded upon the fact that some regular raw cokes, when calcined, possess a substantial degree of needle-like structure or percentage of needle-like particles, for example, typically from about to about This is true regardless of whether the regular coke is petroleum derived or coal tar derived or petrochemical operation derived.

This procedure of mechanical separation and the advantages of same are also applicable to the upgrading of needle-like cokes into even more needle-like or anisotropic cokes. For example, needle-like cokes yielding graphite products with a C.T.E. of between about 8 and about 4X10 inches/inch/ C. contain between about 15% and about 70% of needle-like particles, the rest of particles being considered non-needle-like or substantially round and/or substantially cubical. By separating the needle-like particles from the non-needle-like particles the C.T.E.s of the resultant graphite products can be lowered substantially.

It is known also that some needle-like raw cokes deteriorate during the calcination step because of agglomeration or fusion of the particles. The grinding and screening and separation steps employed in the processes of the present invention serve to counteract and overcome this disadvantageous phenomenon as compared to the processing techniques usually employed in making carbon or graphite articles from needle-like cokes.

It is an additional finding of the present invention that needle-like calcined coke particles may be efiiciently and mechanically separated from the non-needle-like particles of some regular calcined cokes and that if carbon or graphite articles and electrodes are prepared from these separated particles, they will have properties comparable to or competitive with those previously made only from needle-like coke. In other words, it is a finding of the present invention that graphite articles and electrodes having superior properties may be prepared from some regular cokes by using an efiicient, mechanical, postcoking procedure. The advantage of doing this will be apparent from remaining portions of the specification wherein the properties of graphitized electrodes obtained by following the teachings of the present invention are compared with the properties of graphitized electrodes produced from the same regular, calcined coke starting material, but without employing such a mechanical separation procedure.

It is also a finding of the present invention that the properties of graphite articles and electrodes made from needle-like coke may be further improved with regard to C.T.E. and resistivity and other properties by first upgrading the needle-like coke into an even more needle-like or superior coke in accordance with procedures as described herein. The advantage of doing this will also become more apparent from remaining portions of the specification.

It is also a finding of the present invention that by means of techniques such as described herein several types of cokes such as previously described can be adjusted or processed to constant quality levels or to special quality grades. Such processing control is of importance, not only in the making of highly anisotropic electrodes from the needle-like coke, but also to the production of articles out of the non-needle-like coke such as for some types of anodes, some mold stocks, and nuclear applications, wherein the use of coke particles of non-needle-like structure are preferred. In other words, the process of the present invention is able to provide coke particles with controlled needle-like structure and/or coke particles with controlled non-needle-like structure.

BRIEF DESCRIPTION OF THE DRAWING The process, in its essential steps, is illustrated in the accompanying block drawing. It should be appreciated that the process may be carried only as far as horizontal line A-A if the product desired is the separated needlelike or non-needle-like coke, or if, for example the subsequent processing steps are not going to include an extrusion step. Peferably, however, the processing will involve the use of the separated needle-like particles in an extrusion step and then subsequent baking and graphitizing because of the utility and advantages derivable from carrying out this combination of steps. These include the production of baked and graphite electrodes of controlled and high anisotropy, which are conveniently produced on a practical and commercially competitive basis and which oifer superior performance when in use such as in electrode trains in steel furnaces. Other variations of the process are described hereinafter or will be obvious to those skilled in the art.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following examples are set forth to further illustrate the features of the invention and the advantages thereof.

EXAMPLE 1 A sample of calcined petroleum needle" coke was made by coking a clean petroleum residuum in accordance with the procedures of U.S. Pat. 2,775,549. This coke was processed in a typical manner to make a graphite article, i.e. the coke was sized, mixed with a binder, extruded,

baked and graphitized. The particle size of the coke used was as follows:

No. of parts: Size 20 3/+6 (minus 3, plus 6 mesh Tyler screen). 20 10/+16. 20 20/+35.

40 Flour (50% 12% minus 200 mesh).

One hundred parts of this coke was mixed with 27 parts of coal tar pitch binder having a melting point of C. and was extruded into a cylindrical electrode shape with a diameter of 24 inches and a length of 6 feet. The electrode Was then baked to a temperature of 950 C. and graphitized to a temperature of 2800 C. in the usual manner. The graphitized electrode possessed a longitudinal C.T.E. of 6.8 10-' (20100- 0). However, when this needle coke was processed in accordance with procedures of the present invention, i.e. was ground and then screened to obtain tWo fractions, one 6/ +8 Tyler mesh, and the other 8/ +10 Tyler mesh, and these fractions were then cycled through a mechanical separator, the 30% yield of needle-like particles yielded graphite having a C.T.E. of 4x10 (20100 C.) when 60 parts of same were mixed with the same amount of carbonaceous flour and binder as was employed in the control, When extruded, baked, and graphitized under identical conditions as the control. The mechanical separator used was a Simon-Carter (Simon-Carter Co., 655- 19th Ave. NE., Minneapolis 18, Minn), No. 3 Uni-Flow Indented Cylinder Separator using a No. 13 Indent Cylinder. The 30% yield of needle-like particles obtained from the separator was the aggregate material used in the preparation of the electrode. Of the remaining 70% yield of non-needle-like particles from the starting petroleum coke, about one-third of same was further ground to a particle size of about 50% 12% minus 200 mesh Tyler and was used as the carbonaceous flour. (In grinding the non-needle-like particles to a flour a substantial amount of needle-like material was generated.) The remaining fraction of non-needle-like particles was employed for other purposes such as an aggregate in the production of mold stock or in electrodes for the production of aluminum. (In other words, and as previously indicated, the separated non-needle-like particles are not wasted or discarded, but rather may be used for several commercial purposes.)

The graphitized 24" electrode was pre-eminently suitable for use in an electrode train in an electric furnace for the production of steel because of its low C.T.E. and also because it possessed a lowered resistivity in the axial direction.

EXAMPLE 2 A sample of regular calcined petroleum coke when sized and processed as the control in Example 1 resulted in a graphite electrode having a C.T.E. of 12 10- (20- 100 C.). However, when this coke was ground, screened and cycled through a mechanical separator as in Example 1, a 13% yield of needle-like particles was obtained which, when used as the aggregate material in the preparation of an electrode as in Example 1, resulted in a graphite electrode product of 7X10 (20100 C.). As in Example 1, a fraction of the nou-needle-like particles obtained after the separation step was ground into a flour and 40 parts of same were used as the filler (together with 60 parts of the separated needle-like particles) in the preparation of the electrode. The remaining non-needle-like material separated was employed for other purposes.

Also, as in Example 1, the electrode made by following the teachings of the present invention was much more suitable for electric furnace use than was the control electrode.

Other electrodes were made to demonstrate the effects of other processing variables. For example, some electrodes were made wherein a fraction of the yield of needle-like particles was ground and used as the flour material in making the electrodes (rather than a fraction of the separated non-needle-like particles as in Examples 1 and 2). The following table illustrates the results of these tests, as well as some additional processing variables, for the production of large (24-inch) and small (8 inch) diameter electrodes from both needle and regular coke starting materials.

C.T.E.X10- (20l00 C.) of finished S1ze graphite product; electrode Processing conditions, (inehes,, and type aggregate Needle Regular Ex diameter) and/or filler coke coke 3 24 Unprocessed-eontrol; no 7. 2 12 separation; particles and flour. 4 24 Separator used; part of 3. 8 6

needle yield ground into flour; needle particles and needle flour. 24 Separator used; part of 4. 8 8

non-needle yield ground Into flour; needle particles and non-needle flour. 8 Unprocessed; no separa- 6. 5 11 tion; all flour. 8 Separator used; needle 3. 5 5. 5

yield ground into flour; separated needle flour. 8 8 Separator used; non- 7. O 12. 5

needle yield ground into flour; separated non-needle flour.

In the foregoing examples of the table, the use of particles is normal for 24" electrodes and it would be impractical to use an all flour mix in making the large 24" electrodes because of the excessive binder requirements and difficulty of processing. Conversely, large size particles are not usually used in the preparation of small electrodes (e.g. 8" in diameter and under) and consequently all flour mix was used in making the 8 inch electrodes.

There are several ways or pieces of equipment or devices in which the previously discussed mechanical separation step can be carried out. Typically this step or these devices will depend for their operation upon the use of pockets which are sized and shaped to retain the nonneedle-like particles of the calcined coke and to reject the needle-like particles when the pockets are subjected to rotation or vibration. Such pocket separators are well known to those skilled in the mechanical separation art and may be in cylindrical form or disc form or table form. If in cylindrical or disc form they depend upon rotation, and if in table form upon vibration, to eitect the mechanical separation. A cylindrical separator which can be used is described in Example 1. A disc separator which can be used is the Simon-Carter Disc Separator, Size 2527-3. More than one or different types of separators may be used and can be stacked for parallel or series flow to facilitate rapid separation of differently sized coke fractions, or a single piece of equipment can be used with different settings made in same, if necessary, in order to separate screened fractions of different sizes.

The advantages of this invention are particularly notable when the procedures of same are applied to the making of extruded cylindrical graphite electrodes having a diameter of at least 8 inches and more specifically to electrodes which are of fairly large diameter (e.g. between about 16 and about 40 inches) and which are to be used in electric furnaces for the production of steel and wherein they are to carry high currents or subjected to high current densities. In making such electrodes a substantial percentage of the mix used is fairly coarse aggregate.

The process can be used to upgrade or improve any calcined coke starting material which contains a substantial percentage (for example, about 10 to about 70%) of needle-like particles, or to separate any such type coke mixture into two fractions, each of which might be more valuable than the original material. The process is not a substitute for the Shea process of US. Pat. 2,775,549 because by means of that process one can also obtain a graphtie product with a low C.T.E.; but the process of the present invention can be used or carried out in conjunction with the Shea process in order to obtain a better product, or a graphite product with a lower C.T.E. This is important, when the raw material fed into the Shea process is incapable of yielding a C.T.E. as low as desired.

The process of this invention also finds utility in making electrode connecting nipples which characteristically are made from cokes having as low as C.T.E. as, or lower than, the electrodes which they join together. The process is particularly important or advantageous in cases where, for example, one batch of calcined coke yields graphite products with a low C.T.E., e.g. 5Xl0' inches/inch/ C. and another batch yields a graphite product with a higher C.T.E., e.g. 6.5xl0' inches/inch/ C. If nipples made from the latter coke are used with electrodes made from the former coke, this will result in uneven expansion and can cause joint loosening and/or joint splitting problems. The process of this invention, in such a case, can be used to upgrade the latter coke so as to produce nipples from same with axial or longitudinal C.T.E.s nearer to or lower than the C.T.E.s of the graphite products made from the former coke.

It is to be understood that the invention is not limited to the specific examples which have been offered merely as illustrative and that modifications may be made within the scope of the appended claims without departing from the spirit of the invention.

I claim:

1. A process for recovering calcined coke having a relatively high percentage of particles of needle-like structure from an initial mass of calcined coke having a lower percentage of particles of needle-like structure comprising:

(A) Grinding and screening the initial mass of calcined coke to a desired particle size within the range of minus 3 to plus 35 Tyler mesh; and

(B) Mechanically separating the needle-like particles present in the product of step A from the non-needlelike substantially round and substantially cubical particles from said step A by using a device whose 1 operation depends upon the use of pockets sized and shaped to retain the non-needle-like particles and reject the needle-like particles when the pockets are subjected to rotation or vibration.

2. A process according to claim 1 wherein in step A the particles are screened to a series of narrowly sized fractions and wherein in step B the sized fractions from step A are individually mechanically separated into needle-like and non-needle-like particles.

3. A process according to claim 1 wherein the mechanical separation of step B is carried out by using a pocket separator in cylindrical form.

4. A process according to claim 1 wherein the mechanical separation of step B is carried out by using a pocket separator in disc form.

5. A process according to claim 1 wherein the mechanical separation of step B is carried out by using a pocket separator in table form.

6. A process of making a highly anisotropic carbon body which comprises:

(A) Grinding and screening calcined coke, some of which has a needle-like structure, to a desired particle size within the range of minus 3 to plus 35 Tyler mesh;

(B) Mechanically separating the needle-like particles pr sent in the product of step A from the non-needlelike substantially round and substantially cubical particles from said step A by using a device whose operation depends upon the use of pockets sized and shaped to retain the non-needle-like particles and reject the needle-like particles when the pockets are subjected to rotation or vibration;

(C) Mixing the separated needle-like particles from step B with a carbonizable binder;

(D) Extruding the mixture of step C into a green body; and

(E) Baking the extruded green body from step D.

7. A process according to claim 6 wherein in step A the particles are screened to a series of narrowly sized fractions and wherein in step B the sized fractions from step A are individually mechanically separated into needle-like and non-needle-like particles.

8. A process according to claim 6 wherein a carbonaceous flour filler is mixed with the needle-like particles and carbonizable binder in step C.

9. A process according to claim 6 wherein the separated needle-like particles from step B are ground before being mixed with the carbonizable binder in step C and no separated particles are used as such in said step.

10. A process according to claim 8 wherein the carbonaceous flour filler is derived from grinding the separated non-needle-like particles obtained in step B of claim 10.

11. A process according to claim 8 wherein the carbonaceous flour filler is derived from grinding a portion of the separated needle-like particles obtained in step B of claim 10.

12. A process according to claim 6 wherein the extruded green body of step D is cylindrical and has a diameter of at least 8 inches.

13. A process according to claim 12 wherein the extruded green body has a diameter between about 16 and about 40 inches.

14. A process of making a highly anisotropic graphite body Which comprises:

(A) Grinding and screening calcined coke, some of which has a needle-like structure, to a desired particle size within the range of minus 3 to 35 plus Tyler mesh;

(B) Mechanically separating the needle-like particles present in the product of step A from the non-needlelike substantially round and substantially cubical particles from said step A by using a device whose operation depends upon the use of pock ts sized and shaped to retain the non-needle-like particles and reject the needle-like particles when the pockets are subjected to rotation or vibration;

(D) Extruding the mixture of step C into a green body;

(E) Baking the extruded green body from step D; and

(F) Graphitizing the baked body from step E.

15. A process according to claim 14 wherein in step A the particles are screened to a series of narrowly sized fractions and wherein in step B the sized fractions from step A are individually mechanically separated into needlelike and non-needle-like particles.

16. A process according to claim 14 wherein a carbonaceous flour filler is mixed with the needle-like particles and carbonizable binder in step C.

17. A process according to claim 14 wherein the separated needle-like particles from step B are ground before being mixed with the carbonizable binder in step C and no separated particles are used as such in said step.

13. A process according to claim 16 wherein the carbonaceous flour filler is derived from grinding the separated non-needle-like particles obtained in step B of claim 14.

19. A process according to claim 16 wherein the carbonaceous flour filler is derived from grinding a portion of the separated needle-like particles obtained in step B of claim 14.

20. A process according to claim 14 wherein the extruded green body of step D is cylindrical and has a, diameter of at least 8 inches.

References Cited UNITED STATES PATENTS 3,318,447 5/1967 Ellingboe et al 209-213 3,326,796 6/1967 Muller 208--50 2,775,549 12/1956 Shea 208-52 2,922,755 1/1960 Hackley 208-106 X 3,168,509 2/1965 Juel 264-29 X 3,350,485 10/1967 Shesler et al 264- EDWARD J. MEROS, Primary Examiner US. Cl. X.R.